Resolving dependencies... cabal: Could not resolve dependencies: next goal: happy (user goal) rejecting: happy-1.19.5, happy-1.19.4, happy-1.19.3, happy-1.19.2, happy-1.19.1, happy-1.19.0, happy-1.18.11, happy-1.18.10, happy-1.18.9, happy-1.18.8, happy-1.18.7 (constraint from user target requires ==1.18.6) trying: happy-1.18.6 next goal: base (dependency of happy-1.18.6) rejecting: base-4.9.0.0/installed-4.9... (conflict: happy => base<4.5) rejecting: base-4.9.0.0, base-4.8.2.0, base-4.8.1.0, base-4.8.0.0, base-4.7.0.2, base-4.7.0.1, base-4.7.0.0, base-4.6.0.1, base-4.6.0.0, base-4.5.1.0, base-4.5.0.0, base-4.4.1.0, base-4.4.0.0, base-4.3.1.0, base-4.3.0.0, base-4.2.0.2, base-4.2.0.1, base-4.2.0.0, base-4.1.0.0, base-4.0.0.0, base-3.0.3.2, base-3.0.3.1 (constraint from non-upgradeable package requires installed instance) Dependency tree exhaustively searched.